The present invention relates generally to active-matrix liquid crystal display devices and, more particularly, to liquid crystal display devices of the lateral electric field type having wide view-angle characteristics suitable for improvement of the aperture ratio.
Liquid crystal display devices of the active matrix type, which employ active elements typically, including thin-film transistors (TFTS), are becoming more important in the manufacture of display terminals for use with OA equipment in view of the fact that these devices offer enhanced displayability with superior image quality in comparison to cathode ray tubes, not to mention the flatness and light-weight features thereof. Such liquid crystal display devices are generally categorized into two types.
In one type, a liquid crystal material is sandwiched between two substrates, with a plurality of transparent electrodes being arranged thereon, so that application of a voltage to such transparent electrode causes an electric field to be generated transverse to the substrate, thereby modulating rays of light falling onto the liquid crystal after passing through the transparent electrodes, to thereby generate a display—all of the currently available products are designed to employ this scheme.
The other type of device was a scheme for causing the liquid crystal to be modulated by an electric field that is generated substantially in parallel to a substrate surface between two electrodes arranged on the same substrate, thereby modulating light incident on the liquid crystal from a space between the two electrodes, to thereby generate a display in which the viewing angle is extremely wide. This technology, which shows great promise for improvements in active-matrix liquid crystal display devices, is called a “lateral electric field” type or, alternatively, an “in-plane switching” type device.
Some features of the latter type of device have been disclosed in Domestically Published Japanese PCT Application No. 5-505247 Published Japanese Patent Application No. 63-21907 (JP-A-63-21907), and JP-A-6-160878.
However, in the in-plane switching type device, since an opaque metal electrode is arranged into a comb-like shape on one substrate, the resulting ratio of the opening region permitting light to pass therethrough (aperture ratio) is significantly low, which results in the problem that active-matrix liquid crystal display devices of the in-plane switching type have a display screen which is dark, or, alternatively, a bright backlight with great power dissipation must be used in order to brighten the display screen, resulting in an increase in the power dissipation of the devices.
Another problem associated with the in-plane switching type device is that the use of a metal electrode leads to an increase the reflectivity at the electrode, which in turn creates a problem in that an image or the like appears like a ghost image on the screen due to reflection at the electrode, reducing the recognizability of the display.